[aerohead]

Originally Posted by Cd

I was wondering if you guys could post a chart showing the aero penalty for having to use a spoiler / trunk ( boot ) to re-attach the airflow when the rear window angle is not steep enough.

I have seen a couple of cars that had exceptional Cd figures despite having too shallow a curve to the rear window. The cars usually re-attach the air flow at the trunk/boot, or by using a spoiler.

Thanks.

I think we'd have to keep this on a case-specific basis.There are just too many variables which affect the flow back there:
*Length of aft-body (upper) as a function of total body length
*Length of the aft-body (sides) as a function of total body length
*Roof contour/type (flat or curved),notchback/fastback/hatchback
*Presence of upper gaps or not
*Trip strips or not
*Greenhouse tumblehome or lack thereof
*Height of boot with respect to body height
*Length of boot with respect to body height and backlight base
*C-pillar plan-view taper or lack of it
*Submerged backlight
*Flush backlight
*Crowned backlight
*Compound backlight
*Presence of C-pillar buttresses and length
*Body side camber/boat-tailing
*Body edge radii
*Diffuser area architecture
*Spoiler type
*Spoiler position
*Spoiler dimensions
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Hucho insists that the 'fastback' car produces the lowest drag,which infers that any notchback will pay some drag penalty.Depending on the car,this may not be the case for all 'mutilated' bodies.
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I gave up on attempting to cover all aft-body contingencies.Here are a few I looked at



Here are some spoiler examples